It is often necessary to selectively immobilize one member relative to another, and it is often desirable that such immobilization be selectably terminated, so that the member may be adjusted, repositioned, etc. There are a wide variety of mechanisms available which allow one member to be locked into a variety of positions with respect to another.
A subset of such locking members utilizes a rolling member such as a ball which is moveable along a ramp associated with one of the members, and which wedges the members together so that they are immobilized relative to one another. Such devices lock in only one direction since motion of the ball down the ramp will free the members allowing them to move.
The movement of the rolling members between their wedged and free positions are typically accomplished by a complex interaction of mechanical elements. The prior art does not provide a simple locking mechanism by which two members may be reversibly immobilized relative to one another, in two directions of travel.
At least one prior art device attempts to provide a simple locking mechanism utilizing rollers. U.S. Pat. No. 1,390,189 to Bixler et al. discloses a vice post including two telescoping pipes which are releasably locked into position by a locking mechanism or clutch which is carried by the lower section of pipe, the clutch engaging the upper section of pipe. Once locked, the locking mechanism prevents the upper section of pipe from moving downward. The clutch includes a sleeve having a pocket with slots extending at right angles thereto. The pocket and slots extend along the clutch and pipe sections and are inclined inward toward the pipe sections. A roller having a stem extending perpendicularly to the roller and outwardly from the center of the roller is placed in the pocket so that the stem extends through the slots, the roller engaging the lower section of pipe. As the roller is moved downward, the inclined surface of the pocket brings the roller into engagement with the upper section of pipe, wedging the roller between the inclined surface and the upper section, thus preventing downward movement of the upper pipe. To release the upper section of pipe, the stem extending outwardly from the roller is grasped and drawn upward, moving the roller upwardly against the incline and out of engagement with the upper section of pipe. Unfortunately, the Bixler et al. device does not permit easy disengagement of the rolling member from its locked position as the force required to move the rolling member from its locked position is significant. Thus, there remains a need for a simple, hand operable locking mechanism of the aforementioned type which prevents movement in two directions.